Calling all Cahills! Announcing a 39 Clues Superspecial adventure - the gang is back, and called to investigate one of their own: Sinead Starling.

At only seventeen years old, Ian Kabra is head of the Cahills, the most powerful family in the world. He has presidents on speed dial, generals at his beck and call. Ian knows he's an ideal leader and the only man for the job. There's just one small problem: He's already messed up big time. A Cahill from the past calling himself the Outcast has risen to challenge Ian with an impossible test. The Outcast has re-created four of history's greatest disasters and dared Ian to stop him.

Amy and Dan find themselves in a new global race but this time, everything’s different. Those closest to them might be working for the enemy, and Amy and Dan are forced to ask themselves how far they’re willing to go to save the kidnapped Cahills. How much can you risk when there’s no one to trust?

The Cahill family has a secret. For five hundred years, they have guarded the 39 Clues - thirty-nine ingredients in a serum that transforms whomever takes it into the most powerful person on earth. If the serum got into the wrong hands, the disaster would rock the world. So certain Cahills have always made it their mission to keep the serum safe, buried, locked away. Until now. Thirteen-year-old Dan Cahill and his older sister, Amy, are the latest guardians of the Clues. They think they've done everything right, but a tiny mistake leads to catastrophe.

For 500 years, the Cahills have been the most powerful family in the world. For 500 years, they've protected the source of their power - the 39 Clues. And for 500 years, they've kept their secrets silent. Until now. This extraordinary stand-alone novel cracks open the Cahill vault to tell the story of the most coveted piece of artwork in the world, a masterpiece that has been the target of seven separate theft attempts: Jan van Eyck’s altarpiece at Ghent.